Loading and unloading of truck trailers has commonly been practiced manually or with the assistance of various specialized types of forklifts as material handling equipment. These procedures are normally time consuming, expensive and potentially damaging to the goods within the trailer. Moreover, manual handling increases the risk of pilferage, particularly of consumer goods. With the advent of the so-called just-in-time inventory control and management system, the need has arisen for automated handling of trailer carried goods. For example, the automotive manufacture industry is an extensive user of the just-in-time inventory system and requires such components as interior and exterior panels which are placed on racks that are particularly sized and configured for use in the in-plant conveyor material handling system. The racks carrying the panels are typically too large to be manipulated by hand and a forklift and driver unloading operation may be too slow to keep pace with the plant needs. During plant operation, trucks receive an unloading time whereupon they are backed to an unloading ramp, the racks with the components thereon are transferred to the in-plant conveyor and move to a stacker arrangement from which the individual panels are connected to the plant overhead trolley arrangement. Completely automated loading and unloading of the trailer speeds the just-in-time inventory system and lessens manpower requirements, providing increased efficiency and cost savings to the assembly plant and its sub-contractors.
To this end, the instant invention provides a conveyor arrangement comprising a pair of free conveyors mounted to a truck trailer floor adjacent the trailer sidewalls and a middle positioned powered conveyor extending parallel to the free conveyors. The powered conveyor is shiftable upwardly and downwardly to selectively engage a conveyor chain with the bottom surface of an article to be conveyed. The direction of movement is selectable for loading or unloading operations. Although particularly adapted for trailer installations, the instant invention may have applications beyond usage in trailers, such as over and under conveyor systems in buildings.